Big Block Power Combo - Real Fine 509, Part 2

We Put Our Big-Bore Rat On The Dyno To See How Close It Comes To The Bull's Eye Of Dart's Projected Performance.

Last month, we introduced you to our Real Fine 509 Dart big-block buildup. It involved eschewing the conventional wisdom that the way to large displacement performance derives from a long stroke. Instead, we teamed with Dart Machinery to validate the theory that a larger bore and a conventional stroke length was the recipe for outstanding dual-purpose power.

In the previous installment, we followed the assembly of the short-block. With this segment, we finish off the engine and evaluate its dyno performance. In other words, we're going to see how close Dart is to its self-proclaimed bulls eye. Check out www.superchevy.com for a video of the engine on the dyno.

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In the previous installment, we covered the assembly of the short-block, as seen here. It includes Dart's Big M iron cylinder block with 4.500-inch bores and splayed, four-bolt billet steel main caps. To that, an Eagle 4340-forged crankshaft with a 4.000-inch stroke was added, along with forged aluminum JE pistons that were pinned to Engine Pro 6.135-inch-long forged H-beam connecting rods. The result is a super-strong rotating assembly that delivers 509 ci.

It's an amazingly simple combination that relies on no exotic parts, expensive machining or racer secrets. In a nutshell, X+Y=Z, only in our project, our X (the short-block) and Y (the heads/induction system) are really big. In fact, the large volume of the heads, along with a correspondingly-sized intake manifold and camshaft profile, go a long way to maintain robust torque in the engine. Compared with options only a few years ago, larger-volume heads and intakes, with long, straight runners, promote exceptional torque, even with a shorter crankshaft stroke.

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Building on the short-block assembly starts with the camshaft. For better streetability, it's a hydraulic roller from Comp Cams and, with 242/248 degrees of duration at 0.050-inch lift, it's not unruly. To take advantage of the displacement and a set of big-flowing heads, the lift specs are 0.540-inch on the intake side and 0.560-inch on the exhaust. The lobe separation angle is a middle-of-the-road 110 degrees, balancing slightly more valve overlap with a decided lope at idle.

"Torque is something you don't have to worry about with a 509-inch big-block, even with a 4.000-inch stroke," says Maskin. "Sure, you could get more with a longer stroke, but the combination we've laid out here will make more than 600 lb-ft across most of the power band. There's more than enough for any street/strip car."

Those thoughts were confirmed when we viewed the engine's performance on Dart's dynamometer. Right off the bat, it was generating more than 500 lb-ft. In fact, it registered 523 lb-ft at only 2,600 rpm and rose to 600 lb-ft by 3,800 rpm. The torque curve was broad and pretty flat between 2,900 rpm and 6,000 rpm, running between 580 at the low end of the tachometer, peaking at 623 lb-ft at 4,500 rpm and settling back to about 585 at 6,000. And with horsepower simply the product of torque multiplied by engine speed and divided by 5252 (TQ x RPM/5252), as long as the lb-ft readings stayed in that 600 lb-ft range as the revs climbed, achieving our 600hp goal would be a no-brainer.

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Big Block Power Combo - Real Fine 509, Part 2

In the previous installment, we covered the assembly of the short-block, as seen here. It includes Dart's Big M iron cylinder block with 4.500-inch bores and splayed, four-bolt billet steel main caps. To that, an Eagle 4340-forged crankshaft with a 4.000-inch stroke was added, along with forged aluminum JE pistons that were pinned to Engine Pro 6.135-inch-long forged H-beam connecting rods. The result is a super-strong rotating assembly that delivers 509 ci.

Building on the short-block assembly starts with the camshaft. For better streetability, it's a hydraulic roller from Comp Cams and, with 242/248 degrees of duration at 0.050-inch lift, it's not unruly. To take advantage of the displacement and a set of big-flowing heads, the lift specs are 0.540-inch on the intake side and 0.560-inch on the exhaust. The lobe separation angle is a middle-of-the-road 110 degrees, balancing slightly more valve overlap with a decided lope at idle.

With the camshaft in place, a double-row roller timing set is installed. Dart's Big M cylinder block is designed to accept all standard big block components and accessories, so normal, off-the-shelf parts bolt up without a hitch. It will also accommodate belt-drive systems.

A cam thrust button followed up the timing set's installation. Although not always used by many builders, the inexpensive cam button helps ensure the proper end play for the camshaft and prevents cam "walking" under high load.

On the bottom of the engine, a Melling M77HV high-volume oil pump is used. Optimal lubrication is essential in all engines, of course, and the Big M block is designed to take the oil fed by the pump and push to the main bearings first, delivering oil to the most critical areas of the engine first.

The bottom of the engine assembly is finished off with simple, stamped steel oil pan and timing cover. The all-black finish will contrast nicely with the aluminum heads and intake that will come next.

Dart suggested its aluminum Pro1 310cc cylinder heads and we didn't argue. It's the intake runners that measure 310cc, but Dart offers them in capacities up to 345cc. The intake port location is stock to match standard intake manifolds, but the exhaust ports are raised. 0.300-inch for greater flow and the easier installation of larger diameter headers.

The fast burn-style combustion chamber design of the Pro1 heads promotes quicker, more complete combustion. The chamber volume is a relatively larger 121cc. Both the intake and exhaust valves are rolled 2 degrees from stock: 24 degrees vs. the stock 26 degrees on the intake side and 15 degrees vs. 17 degrees on exhaust side. The intake valves measure 2.250 inches in diameter, while the exhausts are 1.880 inches.

Dart threw on relatively new Ultra Pro Magnum roller rockers from Comp Cams (1.7 ratio). Interestingly, they're steel, not aluminum-a feature selected for its strength and long-term durability. In fact, their 8650 chrome-moly steel material is, according to Comp Cams, 300 percent stronger than typical aircraft aluminum rockers. To keep the weight down, they have an open design and the black finish looks pretty cool, we think. Too bad they'll be hidden by the valve covers.

One of the other interesting details of our project engine is the use of Dart's patented, adjustable pushrod guide plates. The self-locking fasteners enable super-easy adjustments with a variety of valvetrain components. Why didn't we know about these years ago?

With the valvetrain set, worked moves to the induction system. It starts with another part designed and manufactured by Dart: the intake manifold. To match the airflow capability of the heads and short-block, it's a cavernous, open-plenum design that shines at high rpm. The raised water crossover and air gap design insulate the air/fuel charge from engine heat, too, while integrated bosses in the runners are there if we ever get the urge to spray our big-block.

For dyno testing, Dart's builders bolted on this Demon 850cfm four barrel. It features 1.560-inch venturis and 1.750-inch throttle blades. Jetting specs include #85 on the primary with a power valve and #93 on the secondary jet and no power valve. The comparatively easy adjustability of the Demon design is appreciated on the dyno.

Here's the completed engine, dressed and ready for testing on Dart's dynamometer. Note the 1-inch spacer between the carb and intake, as well as the 2.125-inch (inside diameter) test headers. And while this engine represents a custom build for Super Chevy, it uses nothing but off-the-shelf parts and Dart's standard short-block components. It could be duplicated with a simple phone call.

The prediction for the engine was 668 hp and after a couple of trial/tuning pulls, the engine cranked out 668 hp. In fact, it was 668.9 at 6,000 rpm. Peak torque was 623 lb-ft at 4,500 rpm. Heck, it was making 500 lb-ft just off idle, so foregoing a longer stroke for larger bores hardly disqualifies this as a torque motor. It just happens to rev easily to 6,400 rpm.

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